German Patent Application No. 40 17 415 and European Patent Application No. 240,049 describe circuit arrangements for starting and operating a.c. high-pressure gas discharge lamps, where the alternating current is obtained from a d.c. source. First, a stabilized and/or power-regulated d.c. voltage is generated from the d.c. voltage of the d.c. voltage source using a DC/DC transformer. Then the alternating current required for operation is generated from this with the help of a bridge circuit. Such an arrangement is expensive and also requires a larger amount of space.
In general, however, in this conventional circuit arrangement, the components used are, first, very numerous and, second, are very large themselves, because they must be designed for operation at low frequencies. This is in conflict in a deleterious manner with the least expensive possible design and operation of such a circuit operation for starting and operating a high-pressure gas discharge lamp.
The arrangements for operation of high-pressure gas discharge lamps in motor vehicles which are on the market operate according to two different principles. With the first principle, both starting and operation take place in the resonance range. The starting frequency, i.e., in starting the lamp, is approx. 80 kHz and the burning or operating frequency is approx. 8 to 16 kHz. According to the other principle, the lamp is operated in intermittent d.c. operation, i.e., the polarity of the direct current is reversed repeatedly. The polarity reversal frequency is approx. 400 Hz. The lamp is started by a separate pulse starter. The lamps are xenon lamps or metal halide lamps whose high pressure is approx. 80 bar. Considering the worst possible tolerance conditions, a high voltage of 24 kV is necessary to start the electric arc. In burning operation, the required voltage is approx. 85 V.
Theoretical disadvantages of these conventional principles are based on the fact that they require a relatively large number of components and a special starter, and furthermore the components are quite large and must be high-voltage resistant. With the arrangement which works according to resonance operation, a particular disadvantage is that it is necessary to work with very high currents in the primary winding because of the voltage source characteristic of the flow transformer. This leads to large components and a relatively poor efficiency. This results in the disadvantages of relatively high cost, high power losses and a considerable amount of space required.